The present invention relates in general to display devices, and in particular, to field emission display devices.
Field emission displays have been previously described as being structured in either diode or triode modes. In a diode mode, the cathode is separated from the anode by a gap. The value of the gap is determined by considering the operating voltage of the phosphor and the turn-on electric field of the electron emitter material (cold cathode). Diode displays can be made with either microtip cathodes or with flat emitters such as carbon-based films. During operation, the gap is fixed by spacers, and the electric current to the phosphor is switched on and off by swing voltages between the anode and cathode. In a passive matrix drive mode, the pixel is off at one-half of the on voltage.
In a triode mode, a grid separates the cathode from the anode. All microtip devices operate in this mode. A triode mode allows a greater degree of flexibility in terms of operating parameters, and the switching voltages can be very low relative to the diode display. In the triode display, a small gap separates the cathode from the grid electrode. This gap is held constant, and the current from the cathode is switched on and off by switching the voltage between the grid and the cathode. The grid allows a significant fraction of the electrons to pass through before they arc and then accelerate to the anode. The acceleration voltage can be very large (5-10 kilovolts or higher) to achieve high phosphor efficiency.